The Irish prime minister, Bertie Ahern, vigorously defended himself from accusations of corruption yesterday as he faced questions at a tribunal investigating payments to politicians in the early 1990s.

In his opening statement to the Mahon tribunal in Dublin, the taoiseach - the most successful since the republic's founding father, Eamon de Valera - denied that he had ever taken a bribe in his 30 years in politics, a career which saw him rise from lord mayor of Dublin to finance minister and eventually to prime minister.

"I have done no wrong and have wronged no one," he said.

During his 15-minute address he came out fighting, claiming that many of the leaks to the Irish media about his personal finances were based on forged documents. He also said that the rumours about his financial affairs were part of a political conspiracy designed to bring him and his ruling Fianna Fáil party down.

Mr Ahern said allegations just before the Irish general election in May this year that he had received a large sum of dollars were "explosive" and purely intended to inflict damage on him and his party. These claims, he said attacked both his honesty and integrity.

Playing on his image throughout Ireland as a plain speaking man of the people, he said he was seeking no special treatment and wished to be treated like any other witness.

He took the stand at mid-morning inside Dublin Castle, the pre-independence seat of British power, and said that during the lifetime of the tribunal no evidence had ever been unearthed to show that he took bribes. But he admitted that while he kept records of utility bills he did not retain receipts of funds he might have received in the 1990s.

Mr Ahern told the tribunal: "I had enough to do" - namely managing the Irish budget as minister of finance. He was responding to claims by an Irish developer, Tom Gilmartin, that a Cork-based builder called Owen O'Callaghan had given bribes to Mr Ahern. These claims were not based on "anything other than hearsay", Mr Ahern said. "I never got a glass of water from Mr O'Callaghan, never mind money," he said.

Des O'Neil, a senior counsel for the tribunal, said the inquiry was concerned with four lodgements connected to Mr Ahern, involving foreign exchange totalling around £85,000 Irish punts back in the mid-1990s. Mr Ahern insisted that one lodgement of almost IR£30,000 in December 1994 had been paid originally in sterling and not dollars, as claimed by the tribunal.

The tribunal insists he received dollar payments, which would have been subject to taxes. Mr Ahern strongly denies this.

He explained some of the lodgements by saying he put IR£30,000 into the O'Connell Street branch of the Allied Irish Bank in Dublin 12 years ago. However the tribunal could not find any record of this.

The tribunal on Wednesday questioned Mr Ahern's former partner, Celia Larkin, who lodged a further IR£29,000 for the then finance minister. Mr Ahern told the tribunal yesterday that this was paid in sterling by a Manchester-based businessman, Michael Wall. Mr Wall was Mr Ahern's former landlord and the money was to refurbish a house that he later rented to the taoiseach.

Mr Ahern said his unusual financial arrangements had resulted from a break-up with his then wife.

The taoiseach is due to give further evidence today. Many of the allegations against him date back nearly a decade and were resurrected during the election campaign. However, despite the media focus on his finances, voters gave him a third term in office as head of a Fianna Fáil and Green party coalition.